Radio transmitter overload protection system



United States Patent 3,182,260 RADIO TRANdMlTTER OVERHEAD PRUTEQTHGN SYSTEM Louis John Heaters-Armstrong, London, England,

assignor to International Standard Electric Corporation, New York, N.Y., a corporation oi Delaware Filed Dec. 4, 1951, cler. No. 156,784 Claims priority, application Great Britain, Dec. 5, 1960, 41,757/6ll 15 Claims. (Cl. 325-151) This invention relates to radio transmitters and more particularly to an overload protection system for radio transmitters to prevent damage to the transmitter tubes in the event of excessive anode current dissipation.

Overload protection systems have taken the form of a relay in the anode or cathode circuit of a transmitter tube which cuts oil the power to the transmitter tubes if the current rises above a predetermined value. This form of overload system suffers from the defect that it" the relay is set to the normal working value of the current when the transmitter is operating correctly, then if the output circuit becomes detuned the normal working current will cause sufficient over-heating of the tubes to damage them. To oi'ercome this deficiency overload protection systems have also been used which operate on the temperature of the anode. In the case of air blast cooled tubes the temperature of the cooling air is used to operate an overload protection system. In the case of a sudden heavy overload the temperature operated protection system may not operate fast enough and damage to the tubes can result.

An object of the present invention is the provision of an improved overload protection system overcoming the above-mentioned and other disadvantages.

According to a feature of the present invention there is provided an overload protection system to disconnect power from the transmitter tubes in the event of excessive anode dissipation comprising a relay device responsive to the dillerence between a current proportional to the power output of the transmitter and a current proportional to the anode-cathode current in a tube of the transmitter.

The above-mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent by reference to the following description taken in conjunction with the drawing, the single figure of which is a schematic diagram of an embodiment of my invention.

Referring to the drawing, tube l is included in the final amplifying stage of a radio transmitter which is driven by a voltage coupled from the preceding amplifier stages (not shown) to the control grid of tube 1. The anode of tube 1 is connected through a suitable choke coil 2 to a source of 3+ potential. A relay 3 having two windings 4 and 5 is arranged to have one of these windings coupled to the anode-cathode circuit of tube 1. As illustrated in the drawing, winding 4 is serially connected into the anode-cathode circuit of tube 1 by connecting winding 4 between the cathode of tube 1 and a reference potential illustrated as ground. The anode of tube 1 is further connected through a coupling capacitor c, a tunable tank circuit 7, a variable inductance 8, a conductor 9, and a coaxial cable 1%) to a suitable load which, for example, may comprise an antenna. In coupled relation with conductor is a device 11 providing an output voltage substantially proportional to the square root of the power fed into coaxial cable ill. The output voltage of device 11 is coupled to one terminal of winding 5 of relay 3 with the other terminal of winding 5 being coupled to a bias source 12 connected to ground, as illustrated, functioning to render the current passing through winding 5 substantially proportional to the power fed to cable it with sufiicient accuracy for the purpose required.

The current passing through windings 4 and 5 of relay 3 are in opposition and will cause the operation of relay 3 to be solely dependent upon the current dissipation at the anode of tube 1 or, in other words, the output power of the transmitter. When relay 3 is operated due to eX- cessive anode dissipation contacts 13 are closed to activate an overload protection device, such as a relay (not shown), to remove power from the transmitter tubes thereby preventing damage to these tubes due to an overload. Thus, relay 3 responds to the difference between the anode-cathode current and a current proportional to the power coupled to the load to activate the overload protection system.

A detailed analysis both mathematically and experimentally relative to device 11 is described in British application No. 31,041/59 new British Patent No. 914,434, issued April 24, 1963. In accordance with the description of this British patent and the drawing of the present application, device 11 includes a toroidal core 14 encircling conductor 9 and a winding 15 disposed on core 14 in a manner whereby conductor 9 and winding 15 form the primary and secondary windings of a current transformer. Winding 15 has disposed in shunt relation therewith resistor 16. Rectifiers l7 and 18 are coupled to the terminals of winding 15 and resistor 16 and the terminals of resistor 19 as illustrated. Also coupled to conductor is a voltage divider including capacitors 20 and 21 directly connected between conductor 9 and ground potential. The junction point between capacitors 2t) and 21 is cou led to the mid-point of resistor 16 to permit the voltage developed across capacitor 21 to be algebraically added to the voltages developed across the two portions of resistor 16.

Capacitor 21 has disposed in shunt relation thereto an inductance 22 which serves as a direct current path between the mid-point of resistor 16 and ground potential.

The voltages V and V present across the two portions of resistor 16 are proportional to the alternating current carried by conductor Q. The voltage V developed across capacitor Ell is proportional to the alternating voltage carried by conductor 9. Since resistor 16 has its midpoint coupled to capacitor 21, the resistance of the two portions of resistor i6 are equal and, hence, voltages V and V present across these two portions of resistor 16 are equal. With winding 15 wound on core 14 to provide the potential polarities as illustrated, the voltage coupled to rectifier i7 is equal to V +V while the voltage coupled to rectifier ll; is V2 V3. The rectified output of rectifier 17 is coupled to output conductor 23 and a predetermined portion of the rectified output of rectifier 13 is likewise coupled to the output conductor 23 which is algebraically combined with the output of rectifier 17. The algebraic combination results in the predetermined portion of the output voltage of rectifier 18 being subtracted from the output voltage of rectifier 17 resulting in a voltage at output conductor 23 substantial- 1y proportional to the square root of the power coupled to the load. It has been found experimentally that if onesixth of the rectified output of rectifier 18 is algebraically combined with the rectified output of rectifier 17 that the resultant voltage output of device 11 will be substantially equal to the square root of the transmitter output power for values of standing wave ratio up to approximately 25. The appropriate positioning of the grounded point of resistor 1? establishes the one-sixth value of the output of rectifier 13 which is combined with the output of rectifier 17 to provide the desired output voltage from device ll.

As pointed out hereinabove, the coupling of a delay 3 ias, as provided by battery 12, in series with winding 5 and output conductor 23 the resultant current flowing in winding 5 will be approximately proportional to the output power fed to the load with suflicient accuracy for the desired overload protection.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. In a radio transmitter, an overload protection system operating to disconnect power from the transmitter tubes in the event of excessive anode dissipation comprising a relay device responsive to the difference between a current proportional to the power output of said transmitter and a current proportional to the anode-cathode current of a tube of said transmitter, said relay device including a relay having two windings, one of said Windings responding to a first current proportional to the anode-cathode current of one transmitter tube and the other of said windings responding to a second current proportional to the power dissipation in the anode circuit of said one transmitter tube, said first and second currents being coupled to said windings in a differential relationship, and contacts operable when said relay is energized to activate an overload protection device.

, 2. A radio transmitter according to claim 1, wherein said second current is obtained from a device including a winding on a toroidal core encircling the output conductor coupled to the anode of said one transmitter tube.

3. A. radio transmitter according to claim 1, wherein said one transmitter tube is the final tube feeding a load.

4. A radio transmitter according to claim 3, wherein said second current is obtained from a device including a winding on a toroidal core encircling a conductor coupled between the anode of said final tube and said load.

5. In a radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being coupled to the anode-cathode circuit of a tube or" said transmitter responsive to the an0de-cathode current, means to produce a current proportional to the power output of said transmitter, and means to couple the current output of said means to produce to the other winding of said relay in adifierential relationship with respect to said anode-cathode current, said relay operating to disconnect power from the transmitter tubes in the event said power output becomes excessive.

6. In a radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being serially connected in the anode-cathode circuit of a tube of said transmitter responsive to the anode-cathode current, cans to produce a current proportional to the power output of said transmitter, and means to couple the current output of said means to produce to the, other winding of said relay in a differential relationship with respect to said anode-cathode current, said relay operating to disconnect power from the transmitter tubes in the event said power output becomes excessive.

7. In a radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being serially connected in the cathode circuit of a tube of said transmitter responsive to the anodecathode current, means to produce a current proportional to the power output of said transmitter, and means to couple the current output of said means to produce to the other winding of said relay in a differential relationship with respect to said anode-cathode current, said relay operating to disconnect power from the transmitter tubes in the event said power output becomes excessive.

8.'In a radio transmitter, an overload protection system comp-risin'g means ccupledto the anode-cathode circuit of a tube of said transmitter responsive to the anode-cathode current, a winding coupled to a toroidal core encircling the output conductor of said transmitter, means coupled in shunt relation to said winding to produce a first voltage proportional to the current flow in said output conductor, a voltage divider coupled to said output conductor to produce a second voltage proportional to the voltage on said output conductor, means coupled to said means in shunt relation to said winding and said voltage divider to algebraically combine said first and second voltages to produce a third volta e proportional to the square root of the output power on said output conductor, means coupled to the output of said combining means to convert said third voltage to a current proportional to said output power, and means to couple the current proportional to said output power to said means responsive in a differential relationship with respect to said anode-cathode current, said means responsive operating to disconnect power from the transmitter tubes in the event said pOWer output becomes excessive.

9. In a radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being coupled to the anode-cathode circuit of a tube of said transmitter responsive to the anode-cathode current, a device including a winding coupled to a toroidal core encircling the output conductor of said transmitter to.

produce a current proportional to the power output of said transmitter, and means to couple the current output of said device to the other winding of said relay in a differential relationship with respect to said anode-cathode current, said relay operating to disconnect power from said transmitter tube in the event said power output becomes excessive.

10. In a radio transmitter, an overload protection system comprising a relay having two windings,one of said windings being serially connected in the anode-cathode circuit of a tube of said transmitter responsive to the anode-cathode current, a device including a winding coupled to a toroidal core encircling the output conductor of said transmitter to produce a current proportional to the power output of said transmitter, and means to couple the current output of said device to the other winding of said relay in a ditlerential relationship with respect to said anode-cathode current, said relay operating to disconnect power from the transmitter tubes in the event said power output becomes excessive.

11. Ina radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being serially connected in the cathode circuit of a tube of said transmitter responsive to the anode-cathode current, a device including a winding coupled to a toroidal core encircling the output conductor of said transmitter to produce a current proportional to the power output of said transmitter, and means to couple the current output of said device to the other winding of said relay in a differential relationship with respect to said anode-cathode current, said relay operating to disconnect power from the transmitter tubes in the event said power output becomes excessive;

5 12. In a radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being coupled to the anode-cathode circuit of a .-tube of said transmitter responsive to the anode-cathode current, a winding coupled 'to a toroidal core encircling the output conductor of said transmitter, means coupled in shunt relation to said winding to produce a first voltage proportional to the current flow in said output conductor, a voltage divider coupled to said output conductor to produce a second voltage proportional to the voltage on said output conductor, means coupled tosaid means in shunt relation to said winding and said voltage divider to algebraically combine said first and second voltages to produce a third voltage proportional to the square root of said output power on said output conductor, means to couple the output of said combiningmeans'to one terminal of the other winding of said relay, and a biasing means coupled to the other terminal of said other winding of said relay to convert said third voltage to a current proportional to said output power, said current proportional to said output power having a differential relationship with respect to said anode-cathode current to operate said relay to disconnect power from the transmitter tubes in the event said power output becomes excessive.

13. In a radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being serially connected in the anode-cathode circuit of a tube of said transmitter responsive to the anode-cathode current, a winding coupled to a toroidal core encircling the output conductor of said transmitter, means coupled in shunt relation to said winding to produce a first voltage proportional to the current flow in said output conductor, a voltage divider coupled to said output conductor to produce a second voltage proportional to the voltage on said output conductor, means coupled to said means in shunt relation to said winding and said voltage divider to algebraically combine said first and second voltages to produce a third voltage proportional to the square root of the output power on said output conductor, means to couple the output of said combining means to one terminal of the other winding of said relay, and a biasing means coupled to the other terminal of said other winding of said relay to convert said third voltage to a current proportional to said output power, said current proportional to said out-put power having a ditferential relationship with respect to said anode-cathode current to operate said relay to disconnect power from the transmitter tubes in the event said power output becomes excessive.

14. In a radio transmitter, an overload protection system comprising a relay having two windings, one of said windings being serially connected in the cathode circuit of a tube of said transmitter responsive to the anodecathode current, a Winding coupled to a toroidal core encircling the output conductor of said transmitter, means coupled in shunt relation to said winding to produce a first voltage proportional to the current flow in said output conductor, a voltage divider coupled to said output conductor to produce a second voltage proportional to the voltage on said output conductor, means coupled to said means in shunt relation to said winding and said voltage divider to algebraically combine said first and second voltages to produce a third voltage proportional to the square root of the output power on said output conductor, means to couple the output of said combining means to one terminal of the other winding of said relay, and a biasing means coupled to the other terminal of said other winding of said relay to convert said third voltage to a current proportional to said output power, said current proportional to said output power having a differential relationship with respect to said anode-cathode current to operate said relay to disconnect power from the transmitter tubes in the event said power output becomes excessive.

15. In a radio transmitter, an overload protection system comprising first means coupled to the anode-cathode circuit of a tube of said transmitter responsive to the anode-cathode current, second means coupled to the output conductor of said transmitter to produce a first voltage proportional to the current flow in said output conductor, third means coupled to said output conductor to produce a second voltage proportional to the voltage on said output conductor, fourth means coupled to said second means and said third means to algebraically combine said first voltage and said second voltage to produce a current proportional to the power output of said transmitter, and means coupled to said fourth means to couple said current proportional to said output power to said first means in a differential relationship with respect to said anode-cathode current, said first means operating to disconnect power from the transmitter tubes in the event said power output becomes excessive.

References Cited by the Examiner UNITED STATES PATENTS 2,504,699 4/50 Kluender 325151 2,509,703 5/50 Stanton 325-151 2,510,519 6/50 Price 325l51 FOREIGN PATENTS 940,239 3/56 Germany.

DAVID G. REDINBAUGH, Primary Examiner. 

7. IN A RADIO TRANSMITTER, AN OVERLOAD PROTECTION SYSTEM COMPRISING A RELAY HAVING TWO WINDINGS, ONE OF SAID WINDINGS BEING SERIALLY CONNECTED IN THE CATHODE CIRCUIT OF A TUBE OF SAID TRANSMITTER RESPONSIVE TO THE ANODECATHODE CURRENT, MEANS TO PRODUCE A CURRENT PROPORTIONAL TO THE POWER OUTPUT OF SAID TRANSMITTER, AND MEANS TO COUPLE THE CURRENT OUTPUT OF SAID MEANS TO PRODUCE TO THE OTHER WINDING OF SAID RELAY IN A DIFFERENTIAL RELATIONSHIP WITH RESPECT TO SAID ANODE-CATHODE CURRENT, SAID RELAY OPERATING TO DISCONNECT POWER FROM THE TRANSMITTER TUBES IN THE EVENT SAID POWER OUTPUT BECOMES EXCESSIVE. 